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Ber. lnst. Geol. Paläont. K.-F.-Univ. Graz
ISSN 1 608-8 1 66
Volume 7
G raz 2003
REEF-CORAL DIVERSITY FROM THE LATE OLIGOCENE
ANTIGUA FM. AND TEMPORAL VARIATION OF LOCAL
DIVERSITY ON CARIBBEAN CENOZOIC CORAL REEFS.
Kenneth G. JOHNSON
Department of lnvertebrate Paleontology, Natural History Museum of Los Angeles County, 900 Exposition
Boulevard, Los Angeles CA 90007, USA.
New collections and continuing taxonomic revision have changed our view of the
Cenozoic history of Caribbean reef-corals. Oligocene to Recent history was characterized by
two episodes of apparently rapid biotic tumover. Previous work has documented in detail a
Plio/Pleistocene transition with extinction of over 50 percent of a Late Pliocene fauna. An
Early Miocene transition remains to be fully documented, but up to one half of the total
number of reef-coral genera recovered from Late Oligocene deposits were extinct by the Late
Miocene (Frost 1 977, Budd 2000). Both transitions included regional extinctions and decrease
in regional coral diversity, but the effects of these extinctions on local reef-coral assemblages
remain unclear. I will examine the community response to these extinctions at the local scale
by comparing ecological diversity of local assemblages from the Late Oligocene Antigua Fm.
with the diversity of Neogene faunules from units in Costa Rica, Curacao, the Dominican
Republic, Jamaica, Panama, and Trinidad.
The reef-coral fauna preserved in the Chattian (Late Oligocene) Antigua Fm. on
Antigua in the Leeward Islands is one important component of the Oligocene Caribbean
regional fauna (Vaughan 1 9 1 9). New collections from the Antigua Formation comprise 542
colonies from 36 collections in 16 localities yielded 45 species from 25 genera including 1 1
species that have not been previously described. Local assemblages from the Antigua Fm.
include between 1 0 and 30 species. However, these richness estimates are suspect because of
uneven sampling among different reef units. Shannon's H and Fishers's a are two other
measures of diversity that might be less subject to sampling effects because they incorporate
information about the abundance distribution within each assemblage (Hayek and Buzas
1 997). Both measures are not correlated with numbers of specimens recovered from the reef
units considered here. Using these measures, there is no significant differences in diversity
between local assemblages in the Antigua Fm. and Neogene local assemblages. Exarnination
of rank abundance plots supports this result.
Local diversity was insensitive to the regional environmental changes responsible for
the Oligocene/Miocene transition on Caribbean reefs, suggesting that there was sufficient
redundancy in the regional fauna to allow functioning local communities to be built from a
reduced species pool.
References
B udd, A. F. 2000 Diversity and extinction in the Cenozoic history of Caribbean reefs. Coral Reefs 1 9:25-35.
Frost, S. H. 1 977. Cenozoic reef systems of the Caribbean -- prospects for paleoecologic synthesis. Pp. 93- 1 00
i n S. H. Frost, M . P . Weiss, and J . B. Saunders (eds.), Reefs and related carbonates - eco1ogy and
sedimentology. AAPG Studies in Geology 4, Tulsa, Oklahoma.
Hayek, L. C. and M. A. Buzas 1 997. Surveying Natural Populations Columbia University Press, New York 563
pp.
Vaughan, T. W. 1 9 19. Fossil corals from Central America, Cuba, and Porto Rico with an account of the
American Tertiary, Pleistocene, and Recent coral reefs. United States National Museum Bulletin 1 30: 1 89524.
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Graz. Austria
August 3-7,
2003
9th International Symposium on Fossil Cnidaria and Porifera